This invention relates to systems and methods for control of fuel delivery to vehicle engines and, in particular, to a system and method for determining the position of a throttle plate of the engine.
A conventional vehicle having a fuel-injected internal combustion engine includes a system for controlling the amount of fuel injected into each cylinder of the engine during a combustion event. The system also frequently includes an electronic throttle control to regulate the amount of air flowing through the engine""s throttle body to the intake manifold and cylinders. Controlling the amount of fuel and air input to the engine cylinders is critical in obtaining an optimal air-fuel ratio in the cylinders and thereby reducing emissions of hydrocarbons (HC), carbon monoxide (CO) and nitrous oxides (NOx).
The electronic throttle control determines the amount of air flowing through the throttle body by determining the angular position of a throttle plate disposed within the throttle body. The position of the throttle plate is determined relative to a closed position of the throttle plate which is used as an index. The closed position of the throttle plate is normally sensed during initial key-on before or at the beginning of ignition of the engine. At relatively high temperatures, the physical geometry between the throttle plate and the throttle body is altered. As a result, the closed position of the throttle plate assumes a different value based on the relatively high temperature of the throttle bodyxe2x80x94a value that is often greater that the values determined for a cooler throttle body.
The engine control system is designed to adaptively learn, over a period of time, corrective terms for predictive idle airflow relative to the closed throttle position. These terms are stored in memory and mature over a relatively long driving period. An error in the corrective terms will therefore result if aberrations in the closed throttle positionxe2x80x94resulting from throttle body temperatures outside of a constrained rangexe2x80x94are not accounted for. For example, an engine control system may learn corrective terms for predictive idle airflow responsive to a closed throttle position determined on a throttle body having a relatively high temperature. If the vehicle is subsequently re-started at a normal temperature, the airflow prediction will be incorrect and will result in the engine speed deviating from the desired engine speed during startup. In some instances, the inconsistent engine speed can even result in a stall.
There is thus a need for a system and method for determining the closed position for a throttle plate in an internal combustion engine that will minimize and/or eliminate one or more of the above-identified deficiencies.
The present invention provides a system and a method for determining the closed position for a throttle plate in an internal combustion engine. A method in accordance with the present invention includes the step of determining a first closed position value. The first closed position value may, for example, be determined using a conventional throttle position sensor. The inventive method also includes the step of estimating a temperature of a throttle body of the internal combustion engine. This temperature estimate may, for example, be made using an air temperature sensor or engine coolant temperature sensor or a weighted combination of the two. Finally, the inventive method includes the step of selecting one value from among the first closed position value and a second closed position value that is stored in a memory. The selection is made responsive to the temperature of charged air and the selected value corresponds to the closed position of the throttle plate.
A system in accordance with the present invention includes a throttle plate position sensor that generates a position signal indicative of a position of the throttle plate and a temperature sensor that generates a temperature signal indicative of a temperature of the throttle body of the internal combustion engine. The system further includes an electronic control unit that is configured, or encoded, to determine a first closed position value responsive to the position signal and to select one value from among the first closed position value and a second closed position value stored in a memory in response to the temperature signal. The selected value again corresponds to the closed position of the throttle plate.
The present invention represents an improvement as compared to conventional systems and methods for determining the closed position of a throttle plate. In particular, the inventive system and method enable corrective terms for predictive idle airflow to be learned without reference to aberrations in the sensed closed throttle position that result from relatively high throttle body temperatures. As a result, the engine control system more accurately predicts airflow to the engine cylinders and maintains consistent speed upon engine startup.
These and other advantages of this invention will become apparent to one skilled in the art from the following detailed description and the accompanying drawings illustrating features of this invention by way of example.